1. Field of the Invention
This invention relates to a method for improving the sharpness of images in photographic light-sensitive elements.
2. Description of the Prior Art
When a photographic image of an object is recored with a black and white light-sensitive element or a multi-color light-sensitive element in which both use a silver halide emulsion, the reproducibility in the fine parts of the object is generally reduced. Such reduction in the sharpness of images is generally attributed to light scattering caused by the silver halide grains present in the layers of the light-sensitive element. In an attempt to prevent such a reduction in the image sharpness resulting from light scattering, there have been proposed, for example, a method wherein the thickness of the coating is decreased, a method wherein the silver halide emulsion grains are finely divided to reduce the light scattering and a method wherein the emulsion layer is dyed with a particular dye stuff. However, the decrease of the coating thickness is limited, for example, by the properties of the light-sensitive element and manufacturing techniques thereof. Furthermore, the method of finely dividing the emulsion grains or by dyeing the emulsion with a dye stuff are, in either case, accompanied by a marked reduction in sensitivity. It is, therefore, extremely difficult to prevent a reduction in the image sharpness caused by light scattering without any deleterious influence.
Furthermore, it is known, in silver halide light-sensitive elements, that their capability of reproducing the fine parts of an object reproduced, that is, the image sharpness, can be improved by the adjacency effect. As herein used, the term "adjacency effect" by which the image sharpness can be improved is intended to describe the phenomenon in which, when an image of a knife edge is formed on a light-sensitive element by exposure, the density in the high density side extremely adjacent to the edge is increased while that in the low density side is descreased, thereby apparently enhancing the contrast of the edge. (See, for example, C. E. K. Mees and T. H. James, The Theory of the Photographic Process, IIIrd E., 521-523, Macmillan Co., 1966).
By suitably utilizing the increase in the edge contrast employing the adjacency effect, the above-described reduction of the image sharpness resulting from light scattering can be compensated for and the capability of reproducing the fine parts of an object to be reproduced can be improved.
As methods for enhancing the image sharpness by the adjacency effect, there have been proposed, at present, for example, a method wherein the development process conditions are improved, for example, by diluting the developer or by using mild agitation during development, and a method in which light-sensitive elements themselves are improved, for example, by usng certain kinds of developing agents as described in U.S. Pat. Nos. 3,297,445 and 3,379,529, or certain kinds of couplers as described in U.S. Pat. Nos. 3,006,759, 3,148,062 and 3,227,554. The compounds used in the last case, however, are unstable or limited in their improvement and therefore the use of such compounds is very often limited.